The present invention relates to hydraulic brake systems, specifically to electronically and microprocessor controlled slave operated hydraulic brake systems that can be used as an independent brake system for towed trailers that operate in conjunction with the towing vehicle brake system.
Typical hydraulic brake technology is based upon the use of a hydraulic accumulator boosted by a hydraulic pump. These brakes are powered and operated by the application of pressurized hydraulic fluid, which is supplied by a hydraulic accumulator. The accumulator is necessary for the brake system to provide a sufficient amount or volume of hydraulic fluid at a high enough pressure to actuate the braking system. In turn, a conventional hydraulic piston pump supplies the pressurized hydraulic fluid in the accumulator. For the accumulator to remain charged, the hydraulic pump must run continuously. Electric power is supplied to the hydraulic pump by the electric power system of the towing vehicle. A problem with typical hydraulic brake technology is that law requires that in the event that a trailer should become unattached from the towing vehicle, i.e., xe2x80x9cbreakawayxe2x80x9d mode, the trailer brake systems must be able to apply the trailer brakes immediately and to keep the trailer brakes applied for 15 minutes. To achieve trailer brake application for 15 minutes, conventional hydraulic brake systems must keep the brake accumulator charged. The hydraulic pump must run for the duration of the fifteen minutes to maintain brake application. During the period of detachment from the towing vehicle, the electric power requirements of the hydraulic pump must be met by a separate battery carried by the trailer as part of the trailer brake system. The separate battery provides power for the brake system to lock the brake down after breakaway. A brake system that is capable of meeting the 15 minute brake application requirement but which does not require continuous running of a hydraulic pump is desirable.
An electrically operated hydraulic brake system is provided that has an electric motor that is mounted on a gear housing. A motor armature preferably has a 3xe2x80x3 shaft with a pinion gear attached to it. The pinion gear comes in contact with a spur gear. The spur gear, on its internal diameter, has an internal acme thread cut into it as an integral part of the gear body. The acme threaded rod has a matching external acme thread cut into its body that threads into the internal acme threads on the spur gear. The acme threaded rod comes in contact with the master cylinder piston assembly. The acme threaded rod is centered within a torque tube by a torque tube bearing. A master cylinder piston assembly is contained within a master cylinder, which also contains hydraulic fluid and a master cylinder spring. A pressure sensor is attached to the master cylinder and measures the hydraulic fluid pressure in the master cylinder chamber. The full reverse travel position of the acme threaded rod is detected by a reverse limit switch, which signals for the electric motor to stop.
A metal enclosure is attached to the gear housing that is attached to a master cylinder adapter to which the master cylinder is attached. Attached to the end of the master cylinder is the pressure sensor. The acme threaded rod extends through the spur gear, and the pinion gear comes in contact with the spur gear. The spur gear and pinion gear operate within the gear housing.
Electrical signals are used to control the slave operated self-contained hydraulic brake system. Three wires communicate the towing vehicle and the slave operated brake system, i.e., the brake system, that communicates electrically with a brake control board. One of these wires is a ground wire, another is a power wire to operate the brake system and the third is the brake signal wire that is used to actuate the brakes. The brake control board has three wires connected to a gear tooth counter, two wires to the brake system backup battery and four wires to control the brake system electric motor. Four additional sensors send signals to the brake control board. The four sensors include the pressure sensor with three wires, the master cylinder fluid level sensor with two wires, a load sensor with three wires and an anti-lock brake sensor with five wires. These sensors provide additional information to the microprocessor to add other control features to the brake system, such an anti-lock braking. The fluid level sensor will facilitate notification of low fluid conditions to the vehicle operator.